The present invention relates to an improvement of a magnetic recording/reproducing apparatus and, particularly, to a magnetic recording/reproducing apparatus suitable to record/reproduce a video signal of wide frequency band, which contains highly fine information.
The so-called video tape recorder (VTR) is well known as a magnetic recording/reproducing apparatus for home use, which utilizes a magnetic tape as a recording medium. In such VTR for home use (referred to as H-VTR hereinafter), in order to realize a long time recording with minimum tape consumption, a low frequency conversion color process is utilized in which a video signal, e.g., NTSC color signal, is divided into a high frequency component including a chrominance signal and a luminance signal and a low frequency component including a luminance signal. The high frequency component is frequency-converted into a low frequency band. The low frequency component is frequency-modulated. The high frequency component whose frequency is lowered and the frequency-modulated low frequency component are added to each other and recorded, as disclosed in Japanese Patent Publication No. 28613/1970.
In the H-VTR of a cross azimuth, guard bandless system, a high frequency luminance signal chroma signal cross-talk between adjacent tracks is prevented by recording the video signal after the high frequency luminance signal is completely removed by passing it through a comb filter. In the H-VTR of a slanted azimuth guard bandless system, a problem of cross-talk between adjacent tracks of the low frequency converted signal is solved by a chrominance signal processing, i.e., the so-called phase shift (PS) processing as disclosed in U.S. Pat. No. 4,178,606, together with the employment of the comb filter in a reproducing operation.
The use of comb filter which removes the luminance signal from the high frequency component causes a horizontal resolution of the video signal which is about 330 lines at an input of the H-VTR to be lowered to 230 to 250 lines.
In order to resolve this problem, it may be possible to record/reproduce the luminance signal of the high frequency component together with the chrominance signal thereof while overcoming the inter-track interference problem by means of a recording system using a guard band. In such case, however, when the respective signal components processed in the respective signal processing systems are combined again, a resultant luminance signal is not always continuous over the whole luminance frequency range due to possible phase difference between the signal components introduced thereinto in the respective processing systems.
Furthermore, for a phase variation introduced by mechanical driving systems of the tape and the head, an output of a reference color subcarrier frequency oscillator is compared in phase with a color sub-carrier of the chrominance signal to control an output frequency of a frequency-conversion local oscillator such that the color signal frequency of the chrominance signal becomes stable during a recovery of the luminance signal in the high frequency component from the reproduced signal by means of the frequency conversion to thereby obtain a satisfactory color image quality (APC system). However, since such time base correction or phase correction is not performed for the luminance signal of the low frequency component, the high frequency luminance signal component and the low frequency luminance signal component, when combined together again, are not always continuous.
In order to resolve the latter problem, it has been proposed to correct the time base variation by obtaining time base variation signal from a reproduced horizontal synchronizing signal or color burst signal and processing it by means of a variable delay line or a digital memory including an A/D converter and a D/A converter. In such system, however, since a S/N ratio of the horizontal synchronizing signal or color burst signal is poor, it is very difficult to correct the time base variation precisely.